1. Field of the Invention
The present invention relates to conductive metal particles, conductive composite metal particles and applied products using these metal particles.
2. Description of the Background Art
In an electric and electronic field, conductive materials containing conductive particles in an insulating organic material have heretofore been widely used for the purpose of achieving electrical connection between circuit devices and electrical connection between wirings in a circuit device.
In mounting of electronic parts on semiconductor integrated circuit boards or the like, for example, surface mounting and COB (chip on board) are utilized for the purpose of mounting electronic parts on a printed circuit board at a high density. In such a mounting method, a conductive adhesive in the form of paste or a film, which contains conductive particles, is used (see Japanese Patent Application Laid-Open Nos. 84716/1985, 231889/1988, 259766/1992 and 75250/1993, etc.).
An anisotropically conductive sheet containing conductive particles in an elastomer is used as a connector for achieving electrical connection between circuit devices, for example, a printed circuit board and a leadless chip carrier, liquid crystal panel or the like. Further, in electrical inspection of a circuit device such as a printed circuit board or semiconductor integrated circuit, it is conducted to intervene an anisotropically conductive sheet between an electrode region to be inspected of the circuit device, which is an inspection target, and an electrode region for inspection of a circuit board for inspection in order to achieve electrical connection between electrodes to be inspected formed on a surface of the circuit device to be inspected and electrodes for inspection formed on the surface of the circuit board for inspection.
As such an anisotropically conductive sheet, there have heretofore been known those of various structures. For example, those obtained by uniformly dispersing metal particles in an elastomer (see Japanese Patent Application Laid-Open No. 93393/1976), those obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating part for mutually insulating them (see Japanese Patent Application Laid-Open No. 147772/1978, etc.), and those with a difference in level defined between the surface of a conductive path-forming part and an insulating part (see Japanese Patent Application Laid-Open No. 250906/1986, etc.) are known.
Further, in double-side printed circuit boards in which wiring layers are formed on both sides of an insulating layer and multi-layer printed circuit boards in which a plurality of insulating layers and a plurality of wiring layers are alternately laminated, columnar conductive materials with conductive particles contained in a curable resin have been used in recent years, in place of plated through-holes (via-holes) as a means for conducting electrical connection between the wiring layers (see Japanese Patent Application Laid-Open Nos. 255982/1996 and 256687/1998, etc.). Since such a conductive material may be formed by filling a conductive paste composition, in which conductive particles are dispersed in a liquid thermosetting resin, into through-holes bored in an insulating layer, and subjecting the conductive paste composition to a curing treatment, electrical connection between wiring layers can be achieved through simple steps, and moreover circuit boards high in connection reliability can be provided because none of chemicals such as a plating solution are used.
In such conductive materials as described above, composite metal particles obtained by plating the surfaces of particles of a metal, for example, nickel, copper or the like with gold high in conductivity and chemically stable are preferably used as the conductive articles.
Such conductive particles are required to provide conductive materials having stable conductivity, specifically to provide conductive materials which have high conductivity and are high in reproductivity thereof. Therefore, conductive particles whose average particle diameter and particle diameter distribution fall within respective particular ranges are used in the production of conductive materials.
However, it has been found that the mere use of conductive particles whose average particle diameter and particle diameter distribution fall within respective particular ranges fails to provide any conductive material having stable conductivity.